What security control provides a method to insure that a transaction did or did not occur?

Identification is the process of asserting an identity, not proving a transaction's occurrence.

Accountability ensures that actions can be traced to an individual, but nonrepudiation specifically prevents the denial of those actions.

Nonrepudiation provides irrefutable proof that a specific action or transaction occurred, preventing a sender from falsely denying they sent a message or a receiver from falsely denying they received it. This is typically achieved through digital signatures or cryptographic hashing combined with trusted timestamps, linking an identity to a specific action, thereby guaranteeing the authenticity and origin of data.

Verification is the process of confirming the truth or accuracy of something, which is a broader concept than preventing repudiation.

Access control restricts who can perform actions on a resource, but it doesn't intrinsically prevent denial of performed actions.